This invention relates to the art of applying plastic foams to a substrate and, more particularly, to a method and apparatus by which the applied plastic foam has a sloping profile in the direction of along the path of application.
The invention finds particular utility in connection with the application of plastic foams to a roof deck and, accordingly, will be disclosed and described in detail herein in connection with such use. At the same time, however, it will be appreciated that the invention is applicable to the applying of plastic foam to substrates other than roof decks.
The spray application of plastic foams, such as polyurethane foams, to an underlying roof substrate is shown, for example, in U.S. Pat. No. 6,036,123 to West and in U.S. Pat. No. 6,024,147 to Hunter, the disclosures of which patents are hereby incorporated herein by reference. The apparatus in the West and Hunter patents comprises a wheeled frame moveable along a path and carrying a foamed plastic dispenser carriage extending transversely of the path and along which a foamed plastic dispenser is displaceable in opposite directions to spray foamed plastic material onto the roof substrate as the frame moves along the path. The frame is driven by an electric motor which, for any given pass along the path is operated at a constant speed which determines the thickness of a layer of the material deposited along the path between beginning and ending ends thereof.
As is well known, most commercial or industrial roofs are flat, whereby standing or ponding water is left in areas of the roof after a rain. Such standing or ponding water reduces the anticipated life of the roofing materials, adds weight to the roof deck, stresses the roof as a result of freezing and thawing cycles, breeds algae and other undesirable plant life, and attracts birds and other animals which drink the water, feed on the algae and the like. Moreover, many rooftop-mounted air-conditioning units draw outside air from the roof area, and algae or mold growth resulting from stagnant water on the roof surface has the potential for contaminating the air or producing an unpleasant odor within the building. Further, standing water makes maintenance of the roof and repairs thereto very difficult and creates an unsafe condition for maintenance personnel walking on the roof. Still further, in the event of a leak in the roof beneath an area of standing water, the potential for interior damage is greatly increased over that which might result from rain water running across the area but off the roof surface. The likelihood of ponding water increases as a building ages due to, for example, deflection in the roof deck, and the weight of standing or ponding water may increase to the point where it creates a safety hazard. For example, a 25,000 square foot roof with two inches of ponding water adds approximately 5,000 lbs. of weight to the roof deck. Moreover, the weight of standing water can crush the insulation located under the waterproofing membrane on the roof, thus reducing the R-value of the insulation and increasing the cost of heating and cooling the building. Crushing of the insulation can also increase the depth of the standing water and if the waterproofing membrane is breathable, such as silicone, acrylic or the like, the hydrostatic pressure of the standing water can saturate the underlying insulation. Standing water also adversely affects the adhesion of many protective coatings commonly used on flat roofs.
Heretofore, efforts to eliminate standing or ponding water and to produce positive water drainage on a flat roof surface have included the manufacturing of tapered insulation boards at a factory or the like, laying the boards out in multiple layers on a roof surface, and mechanically attaching the boards to the roof surface such as by screws and hold-down plates. The tapered boards are then covered with a water proofing membrane. This process is very labor intensive and expensive, and the cost is increased when laying the insulation boards over a roof deck which will not accept nails, such as concrete, gypsum and the like. Another effort, as shown in the patent to Hunter, involves the laying of multiple flat layers of polyurethane foam in which each of the layers is of uniform thickness relative to the underlying roof deck in the direction of application. Laterally adjacent ones of the layers are of different thickness relative to the deck, whereby the layers are terraced. This process is also time-consuming and thus expensive and, moreover, produces long lengths of flat surfaces which can be several feet wide, thus creating the potential for the undesired standing or ponding of water on the flat surfaces.